1. Field of the Invention p The present invention relates to a gas component detector which may suitably be used in exhaust gas purifying systems employing a three-way catalyst for automobiles.
2. Description of the Prior Art
As gas component detectors conventionally known include those disclosed in Japanese Utility Model Laid-Open applications No. 46781/77 and No. 46792/77. These detectors are typically constituted by a detector element having a sintered body of a transition metal oxide, a pair of electrodes buried in the detector element, and a ceramic body having a pair of narrow penetrating holes to accomodate therein the pair of electrodes and having a pair of large penetrating holes to accomodate therein a pair of lead pins for delivering a signal indicative of a change in resistance value of the detector element. And a conducting glass is used between the electrodes and the lead pins to obtain electrical conduction therebetween. Further, the detectors have a housing with threads to enable them to be mounted on an exhaust pipe or the like.
By further study of the gas component detectors having the construction conventionally known as mentioned above, it has been found that several problems as follows still exist:
(1) The conductive glass is used to connect electrically the lead pins and the electrodes. However, since it is necessary to push in the lead pins and to appply pressure on the conductive glass at the melting time of the conductive glass for the purpose of filling the conductive glass uniformly in the connecting portion, lead pins having a large diameter must be used in order to widen an area under pressure. Thus, a large ceramic body is needed, and consequently, the construction of the detector itself becomes large.
(2) The ceramic body and the housing are fixed by caulking using a washer and a ring, therefore, the caulking force is apt to be insufficient, becomes loose and thus insufficiently airtight, and also sometimes the ceramic body or the detector element are broken at the time of caulking.